1. Field of the Invention
The present invention relates to cathode ray tube (CRT) displays. In particular, the present invention is drive circuitry for driving a CRT at very high speeds.
2. Description of the Prior Art
Cathode ray tube (CRT) display monitors have found increasing use in various fields of information processing. Because CRT monitors can display full pages of readable information, there is an increasing demand for high performance CRT monitors for word processing, graphics, electronic document storage and retrieval, and other electronic information processing applications.
One important application of high performance CRT monitors is in word processing equipment. There is an increasing trend toward word processing equipment in which an entire page is displayed. This permits the operator to see an image of what will be printed, before it is printed. From a human engineering standpoint, a page image with black characters on a white background provides the operator with the best page image display possible, since it most closely approximates the appearance of the finished product.
Another important application of high resolution, high density CRT monitors is in computer based systems which provide facsimile (FAX) type displays. In this application the actual image of the page of paper, including photos, signatures, drawings, diagrams and handwritten messages, is displayed. The source of data may be a "FAX" machine, a video disk (or other laser based encoding-decoding equipment), a standard computer data base, or a high resolution camera. Operation of this equipment, however, is predicated upon the availability of high resolution, high density CRT monitors.
Another important application for high resolution, high density CRT monitors is in photocomposing systems. The very nature of the photocomposing task virtually demands a page image display as an integral part of the photocomposing system.
High resolution, high density CRT monitors have been developed in recent years which operate at horizontal scan rates which are much higher than the industry standard 15.75 KHz. These monitors include the Motorola M4408, the CPT Corporation HRD15 and the Video Monitors Inc. M15A60.
The Motorola M4408 is an interlaced unit having a horizontal scan rate of 34 kHz and a video bandwidth of 50 MHz. Since it is an interlaced unit, the M4408 requires a slow response yellow-green T19 phosphor, which limits its resolution and contrast. In addition, the M4408 is relatively bulky, complex and expensive.
The CPT Corporation HRD15 has a horizontal scan rate of 50 kHz and a video bandwidth of 100 MHz. While providing high performance, the CPT HRD15 is complex and expensive.
The Video Monitor M15A60 has a horizontal scan rate of 50 kHz and a video bandwidth of 85 MHz. While providing high performance, it is also relatively complex and expensive.
There is a continuing need for a high performance CRT monitor capable of operating at high scan rate with high resolution, while being less complex and expensive than the prior art high resolution, high density CRT monitors.